This proposal is a second revision of a project whose principal aims are to examine the developmental progression of the circadian timing system (specifically intrinsic circadian period) across adolescence into young adulthood, to evaluate intrinsic period in adolescents with Delayed Sleep Phase Syndrome (DSPS), and to examine potential gene associations with the circadian timing system and sleep regulatory process. Adolescent human development is characterized by a significant delay in the timing of sleep, which has serious consequences for teens living in modern society: many teens are sleep deprived and at risk for mood problems. The revised proposal examines sleep/wake processes in maturing adolescents and young adults for developmental changes in regulatory mechanisms that may relate to the phase delay of sleep. Teens with delayed sleep phase syndrome (DSPS) are also studied, and genetic associations are examined. Study 1 examines the hypothesis that intrinsic circadian period lengthens across adolescent development and then shortens in young adulthood. Period is assessed with 28-h forced desynchrony in a new sample of prepubertal youngsters followed at pubertal maturation, and in returning adolescents and young adults from previous samples. The intensive investigation requires participants to keep a fixed sleep-wake schedule at home for at least two weeks and then to live in the laboratory for 15 consecutive days and nights under specific testing conditions to measure sleep, melatonin secretion, mood, and performance. Study 2 uses the same measures to look at adolescents diagnosed with DSPS, a major sleep disorder often associated with mood and behavior problems. The study tests the hypothesis that intrinsic period is longer in adolescents with DSPS and/or that they differ in the nocturnal decay of sleep pressure (slow wave activitivity, SWA). Comparisons are made to the controls in Study 1 matched for age and pubertal stage. Study 3 is a pilot investigation of genetic associations for whether the endophenotypes described in Studies 1 and 2 (e.g., intrinsic period, sleep pressure) can be attributed to specific variations in target genes. Patients and healthy participants will be compared; developmental changes will be examined as well. PUBLIC HEALTH RELEVANCE: This research project will help explain a major change in teens' sleeping behavior which often leads to sleep deprivation and mood problems by looking at how the body's biological sleep regulation systems change during puberty and young adulthood. Teens with a major sleep disorder, Delayed Sleep Phase Syndrome (DSPS), may show extreme differences from the healthy youngsters. Basic knowledge gained and discovery of genetic associations with these biological processes can help target ways to improve teen sleep and waking behavior and may even help with treatment for DSPS and other adolescent sleep disorders.